1. Technical Field
Embodiments of the present invention generally relate to a developing device, a process cartridge, and an image forming apparatus, such as a copier, a printer, a facsimile machine, or a multifunction machine (i.e., a multifunction peripheral) having at least two of copying, printing, facsimile transmission, plotting, and scanning capabilities, that includes a developing device.
2. Description of the Related Art
Generally, image forming apparatuses include a developing device to develop latent images formed on a latent image bearer with developer. For example, there are two-component developing devices that employ two-component developer consisting essentially of toner particles and carrier particles to develop the latent image on the latent image bearer. In two-component developing devices, a range where a developing sleeve, serving as a developer bearer, faces the latent image bearer, such as a photoreceptor, is called a development range. A magnetic field generator provided inside the developing sleeve generates a magnetic field that causes developer particles to stand on end, in the form of a magnetic brush, on the developing sleeve, and the magnetic brush contacts the latent image bearer in the development range. Thus, toner is supplied to the latent image on the latent image bearer, developing it into a toner image.
Additionally, on the surface of the developing sleeve downstream from the development range in the direction in which the developing sleeve rotates, the magnetic field generator exerts magnetic force to separate carrier particles from the developing sleeve. At that time, toner particles adhering to the carrier particles leave the developing sleeve as well. As the developing sleeve rotates further, the surface of the developing sleeve reaches a developer supply position where the developing sleeve is supplied with developer.
In such two-component developing devices, it is possible that history of a preceding image is inherited to a subsequent image, and the amount of toner on the latent image bearer fluctuates, resulting in image failure called “ghost images”, in which image density fluctuates.
For example, in ghost images (also called “afterimages”) that arise when solid images are formed by the two-component developing device, the image density is higher in a portion corresponding to a first rotation of the developing sleeve. It is known that the ghost image may be caused by the developer used for the preceding image and remaining on an outer surface of the developing sleeve. Ghost images may be inhibited by reducing the amount of developer remaining on the outer surface of the developing sleeve. For that, it is conceivable that the developing sleeve is provided with a low friction surface layer lower in friction coefficient with toner than a base material of the developing sleeve.